Point‐to‐axis optical activity induction in extended, sterically congested chromophoric systems

The readily available, modular and electronic circular dichroism (ECD)-silent derivatives of terephthalaldehyde (the probes) have exhibited an induced optical activity upon condensation with chiral primary amines. The central unit of the probe serves as an amine binder by forming imine bonds and is flanked by two extended chromophoric units (“the wings”). Modification of the wings by diphenylamine or carbazole units affects the sterical and spectroscopic properties of the probes. An increase in sterical congestion within the probe core resulted in a change in the mechanism of optical activity induction. In the more congested systems, the point-to-axial chirality transmission from the chiral amine (the inducer) to the chromophoric system led to the adaptation of helical conformation by “the wings” and the appearance of non-zero Cotton effects (CEs) in the low-energy part of the ECD spectrum. However, the sterically congested probes were sensitive to the chirality of the inducers but relatively indifferent to the differences in their structure. Thus, the chirality of the inducers triggers conformational change towards the thermodynamically preferred conformational diastereoisomer due to the probe's —1 - +1 operation scheme.